Two stage refrigeration compressor having automatic oil drain for the first stage suction chamber



United States Patent Inventor Appl. No. Filed Patented Assignee TWO STAGE REFRIGERATION COMPRESSOR HAVING AUTOMATIC OIL DRAIN FOR THE FIRST STAGE SUCTION CHAMBER 6 Claims, 4 Drawing Figs.

US. Cl 184/6, 62/84 Int. Cl .tFl6n 17/06; F25b 43/02 Field of Search 184/6 (lnquired); 230/206, 207

[56] References Cited UNITED STATES PATENTS 2,646,212 7/1953 Kellie 230/206 2,818,210 12/1957 Philipp 230/206 Primary Examiner-Robert M. Walker Attorney-James E. Nilles ABSTRACT: Means for automatically draining the oil from the first stage suction chamber to the crankcase of a two stage refrigeration compressor. The first stage suction chamber is at a lower pressure than the crankcase, but the present draining means nevertheless permits draining of suction chamber oil due to the action' of a float switch which in turn actuates a solenoid controlled valve that equalizes pressure between the first stage suction chamber and the oil collecting tank, to permit draining.

TWO STAGE REFRIGERATION COMPRESSOR HAVING AUTOMATIC OIL DRAIN FOR THE FIRST STAGE SUCTION CHAMBER BACKGROUND OF THE INVENTION In refrigeration compressors having two stages, that is, an internally compounded compressor having at least two sets of cylinders which operate at different pressure levels, the crankcase of the compressor is at the same pressure as one of the cylinders. The reason the crankcase pressure is maintained at the same pressure as the suction of the second stage is that the compressor bearing and pistons are not overloaded as they would be in the event the crankcase pressure were maintained at a much lower level and equivalent to the first stage suction pressure. Thus, it has been a problem as to how to handle the oil or any other liquid that might collect during the normal operation in the first stage suction chamber, since this chamber is at a pressure that is below the crankcase pressure and a simple draining method cannot be used, Heretofore, one way to drain the oil'which had accumulated from the first stage suction chamber was shut down the compressor and permit the pressures within the compressor to equalize internally, thereby permitting the oil to drain through a check valve which is located between the first stage suction chamber and the crankcase.

Certain other prior art devices have utilized compound compressors with check valves or some other pressure sensing devices located between the crankcase and the first stage suction chamber, and the arrangement is such that when the com pressor is in operation, the check valve or regulating device closes and isolates the high pressure crankcase from the low pressure first stage suction chamber.

Halocarbon refrigerants or similar refrigerants in which oil is miscible and carried along through the refrigeration system with the refrigerant, the oil will separate and collect in the first stage suction chamber and the level will continue to increase while the compressor is in continuous operation. This increase in the oil level in the first stage suction chamber is detrimental in several aspects. The crankcase level will be reduced by the amount of oil that collects in the first stage suction chamber and possibly would reach such a low level that the unit would fail or otherwise be shut down because of the action of an oil pressure sensing safety switch. Another undesirable result is that when the level get high enough, which it frequently does with continuous operation, oil in large quantities will begin to carry through into the cylinders in surges and the hydraulic forces a can severely damage or result in failure of the first stage valve plates, pistons and associated parts.

One of the limitations of prior compound compressor designs is that the compressor must be shut down periodically in order for the pressure inside of the compressor to equalize and thereby permit the check valve to open and consequently the oil to drain from the first stage suction chamber back into the crankcase. Because Halocarbon refrigerant systems in themselves are not predictable as to the quantities of oil and circulation rate of oil, the frequency of shut down for this purpose is not readily determined. Because of this limitation, severe restrictions of the application for which a compound compressor can be used are the result, and prevent its use on industrial type applications where a compressor must operate continuously throughout the year.

SUMMARY OF THE INVENTION The present invention provide provides a two stage refrigeration compressor having automatic oil drain for the first stage suction chamber and in which the draining of the oil takes place automatically and transfers the oil from the collecting tank that is in communication with the suction chamber and back into the crankcase. This transfer occurs as frequently as necessary and depends on the amount of oil that collect in the collecting tank. More specifically, the collecting tank has a float switch which initiates the transferring cycle whenever necessary, and the arrangement is sufficiently flexible so it will match the variations in oil return rates for the various types of refrigeration systems. As a result, the arrangement prevents oil in the first stage suction chamber and the undesirable damage to the compressor parts, and furthermore permits an a much wider use of this type of compressor.

The present invention provides an automatic draining arrangement which drains the oil out of the first stage suction chamber, which chamber is at a lower pressure, and into the higher pressure crankcase, permitting continuous operation of the compressor.

These and other objects and advantages of the present invention will appear hereinafter as this disclosure progresses, reference being had to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a more or less schematic diagram of the automatic drain of the invention as applied to a refrigeration system, and in which two solenoids are used; FIG. 2 is an electrical diagram used with the invention; FIG. 3 is a view similar to FIG. 1, but shows a single solenoid arrangement;

FIG. 4 is an electrical diagram of a circuit used in the FIG. 3 modification.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a refrigerating system including a conventional condenser 6, evaporator 7, receiver 8, expansion valve 9, and a two stage compressor 10 having a first stage suction chamber 11 and a crankcase chamber 12.

The first stage suction chamber 11 of the compressor is at a lower pressure than the crankcase chamber 12 and consequently it has heretofore been difficult to drain oil from the low pressure suction chamber into a higherpressure crankcase, particularly under continuous operation conditions.

The two stage compressor also has other chambers such as the first stage discharge chamber D1, second stage suction chamber S2 connected via opening 13 to the crankcase chamber 12, and a second stage discharge chamber D2. The first stage suction chamber 11 is at a relatively low pressure; the first stage discharge chamber 01, the second suction chamber S2, and the crankcase 12 are all at an intermediate pressure; and the second stage discharge chamber D2 is at a relatively high pressure.

In accordance with the present invention, a collecting tank 14 has been provided and is placed in communication with the low pressure suction chamber via a conduit 15, in which a solenoid operated valve 16 is interposed. The collecting tank also communicates with the crankcase chamber via conduits 18, in which a solenoid operated valve 19 is interposed. These solenoid valves, as shown in FIG. 2, have coils 16a and 19a respectively.

A float switch FS is located in the collecting tank and is located in the electrical line 20, and has been shown as a float with a high level switch. Of course, a float switch with a high and a low switching action could be used.

An electric heater H, which is thermostatically controlled, may be positioned in the collecting tank to remove liquid refrigerant before being pumped into the crankcase.

As further shown in the electrical diagram of FIG. 2, a control relay CR is provided as is a timer TR.

The operation of the system is as follows: The solenoid valve 16 is normally open and oil drains from the first stage suction chamber 11 and into the collecting tank until the float switch closes. Up until this time the valve 19 has been closed. When the float switch closes, the solenoid 16 also closes and at the same time solenoid 19 opens, thus allowing the collecting tank 14 to equalize in pressure to that of the pressure in crankcase chamber 12. The oil then drains by gravity to the crankcase chamber 12 while the timer holds the valve 19 open. After a predetermined time the valve 19 closes and valve 16 opens, thereby placing the arrangement in condition for another draining cycle.

The one solenoid arrangement shown in FIG. 3' has a generally similar collecting tank 14 and a float switch FS. A conduit 30 connects'the first stage suction chamber 11 to the collecting tank 14 through a one way check valve 31. The bottom of the collecting tank is connected via conduit 33 to the crankcase chamber 12, and the one-way check valve 34 is interposed in line 33. A third conduit 36 connects the second stage discharge chamber D2 with the collecting tank 14 and this line has an orifice restriction 38 interposed therein and also a solenoid valve 39 located ahead of the orifice. Third conduit 36 is shown as connected to conduit 31 so that both conduits enter tank 14 together.

The arrangement is such that the oils drains via line 30 through the one-way valve 31 and into the collecting tank 14 until the float switch FS actuates the solenoid valve 39 to thereby vent the second stage discharge pressure of chamber D2 into the collecting tank 14. The timer then holds the solenoid 39 open for a period of time to force oil from the collecting tank into the crankcase chamber 12 via conduit 33 and check valve 34.

Check valve 31 has a slight leakage provided in it to thereby equalize the pressure in the collecting tank 14 to that of the first stage chamber 11 when the solenoid 39 closes. Because the check valve 31 has controlled leakage after the oil collecting tank has drained and the solenoid valve 39 has closed, the pressure in the oil collecting tank will then slowly reduce through this controlled leakage arrangement of check valve 31, until the pressure in the oil collecting tank is the same as the low pressure in the first stage suction chamber. The oil then, due to gravity head, will open check valve31 and the oil will flow into the collecting tank to once again fill the tank and repeat the cycle.

There is one advantage of the FIG. 3 arrangement over the FIG. 1 arrangement. in the HO. 1 device the crankcase oil level is located below the oil collecting tank so that it is possible to drain by gravity to the crankcase. The arrangement shown in FIG. 3, however, illustrates that the crankcase can be above the level of the oil collecting tank and this is possible because the pressure from the discharge chamber D2, when solenoid valve 39 is open, provides sufficient pressure in the oil collecting tank above the oil level to force the oil through the drain line check valve 34 and the connecting line 33 and into the crankcase. ln many installations, it may be more convenient when packaging the complete refrigeration system to locate the oil collecting tank at a level well below the compressor which would provide an improved gravity drain for filling the oil collecting tank and still permit pressurization for emptying the collecting tank to force the oil into the elevated crankcase.

RESUME The present invention provides a two stage compressor which includes a first stage suction chamber that is at a lower pressure than the crankcase chamber, and in which the oil can be automatically drained from the first stage suction chamber back to the crankcase chamber without interrupting the operation of the compressor. The transfer of fluid occurs as needed and the arrangement is flexible to a accommodate variation in the rate of oil return for the different types of refrigeration systems. By means of the collecting tank including the float operated valve having an electrical connection with solenoid operated valves in the conduits between the compressor and collecting tank, the pressure in the collecting tank is changed so as to permit draining of the oil from the suction chamber to the collecting tank and then when that phase is completed, it is changed to cause flow of the oil from the collecting tank to-the crankcase.

1. In a refrigerating system having a condenser an evaporator, a receiver and a two stage compressor, said compressor including a first stage suction chamber and a crankcase chamber, said crankcase chamber being at a higher pressure than said first stage suction chamber, means for automatically draining oil from said first stage suction chamber and to said crankcase chamber and comprising a collecting tank, float valve means in said tank, first conduit means placing said suction chamber in oil delivering communication with said collecting tank, second conduit means placing said suction chamber in oil delivering communication with said crankcase chamber, solenoid valve means connected with at least one of said conduit means, and an electrical circuit including said float valve means, said solenoid valve means and a timer, whereby the oil in said suction chamber can drain to said col lecting tank by gravity for accumulation therein and actuation of said float valve means, said float valve means actuating said solenoid means to permit oil to flow from said collecting tank to said crankcase chamber.

2. A two stage compressor including a first stage suction chamber and a crankcase chamber, said crankcase chamber being at a higher pressure than said first stage suction chamber, means for automatically draining oil from said first stage suction chamber and to said crankcase chamber and comprising, a collecting tank, float valve means in said tank, first conduit means placing said suction chamber in oil delivering communication with said collecting tank, second conduit means placing said collecting tank in oil delivering communication with said crankcase chamber, solenoid valve means connected with a least one of said conduit means, and an electrical circuit including said float valve means, said solenoid valve means and a timer, whereby the oil in said suction chamber can drain to said collecting tank by gravity for accumulation therein and actuation of said float valve means, said float valve means actuating said solenoid means to permit oil to flow from said collecting tank to said crankcase chamber.

3. A two stage compressor including a first stage suction chamber and a crankcase chamber, said crankcase chamber being at a higher pressure than said first stage suction chamber, means for automatically draining oil from said first stage suction chamber and to ,said crankcase chamber and comprising, a collecting tank, float valve means in said tank, first conduit means placing said suction chamber in oil delivering communication with said collecting tank, second conduit means placing said collecting tank in oil delivering communication with said crankcase chamber, solenoid valve means connected in said first conduit means, another solenoid valve means connected in said second conduit means, and an electrical circuit including said float valve means, said solenoid valve means and a timer, whereby the oil in said suction chamber can drain to said collecting tank by gravity for accumulation therein and actuation of said float valve means, said float valve means actuating said s solenoid means to permit oil to flow from said collecting tank to said crankcase chamber.

4. The arrangement as defined in claim 3 further characterized in that said solenoid valve means in said first conduit means is normally open, and when said float valve means is actuated, said solenoid valve means in said first conduit closes and said another solenoid valve means opens.

5. A two stage compressor including a first stage suction chamber and a crankcase chamber, said crankcase chamber being at a higher pressure than said first stage suction chamber, means for automatically draining oil from said first stage suction chamber, and said crankcase chamber and comprising, a collecting tank, float valve means in said tank, first conduit means including a one-way check valve and placing said suction chamber in oil delivering communication with said collecting tank, second conduit means including a oneway check valve and placing said collecting tank in oil delivering communication with said crankcase chamber, a third conduit means including a solenoid valve means connected with said collecting tank for conducting pressure thereto, and an electrical circuit including said float valve means, said solenoid valve means and a timer, whereby the oil in said suction chamber can drain to said collecting tank by gravity for accumulation therein and actuation of said float valve means, said float valve means actuating said solenoid means to permit oil to flow from said collecting tank to said crankcase chamber.

6. An arrangement as defined in claim 5 further characterized in that in that said float valve means actuates said sole- 

